re-use of wrong HTTP NTLM connection

VULNERABILITY

libcurl can in some circumstances re-use the wrong connection when asked to
do an NTLM-authenticated HTTP or HTTPS request.

libcurl features a pool of recent connections so that subsequent requests
can re-use an existing connection to avoid overhead.

When re-using a connection a range of criterion must first be met. Due to a
logical error in the code, a request that was issued by an application could
wrongfully re-use an existing connection to the same server that was
authenticated using different credentials. One underlying reason being that
NTLM authenticates connections and not requests, contrary to how HTTP is
designed to work and how other authentication methods work.

An application that allows NTLM and another auth method (the bug only
triggers if more than one auth method is asked for) to a server (that
responds wanting NTLM) with user1:password1 and then does another operation
to the same server with user2:password2 (when the previous connection was
left alive) - the second request will re-use the same connection and since
it'll then see that the NTLM negotiation is already made, it will just send
the request over that connection thinking it uses 'user2' credentials when
it is in fact still using the connection authenticated for user1...

Two common auth defines in libcurl are CURLAUTH_ANY and CURLAUTH_ANYSAFE.
Both of them ask for NTLM and other methods and can therefore trigger this
problem.

Applications can disable libcurl's re-use of connections and thus mitigate
this problem, by using one of the following libcurl options to alter how
connections are or aren't re-used: CURLOPT_FRESH_CONNECT,
CURLOPT_MAXCONNECTS and CURLMOPT_MAX_HOST_CONNECTIONS (if using the
curl_multi API).

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2014-0015 to this issue.

CWE-305: Authentication Bypass by Primary Weakness

AFFECTED VERSIONS

This flaw has existed ever since libcurl started to support NTLM, although
the code has been restructured a few times over the years so the mistake has
altered shape over the years.